This invention relates generally to improvements in video recorder-playback machines, and more specifically, to an improved rotatable drive spindle assembly for smooth relatively high speed rotation of a video information disc in a video recorder-playback machine.
Video recorder-playback machines in general are known in the art and include appropriate means for recording and/or playing back a video information signal utilizing a selected medium for storage of the signal. For example, in one type of machine, the video signal is recorded magnetically for storage and/or retrieval upon a length of so-called video tape. In another type of system, the video signal is recorded upon an information disc for retrieval by means of a stylus, in a manner generally analogous to that of sound reproduction from phonographic records. In still another type of system, the video signal is used to frequency modulate a beam of amplified light, such as a laser beam, with sufficient power for physically altering the surface characteristics of a light sensitive coating on a video information disc and thereby record the signal upon the disc. During playback, a lower power light beam is reflected from the disc and the resulting signal is demodulated to reproduce the recorded signal. In all of these types of systems, the video information signal can be combined with an appropriate audio signal for either recording or playback purposes to yield a composite audio-video signal of the type commonly used for television transmissions and the like. For convenience, however, the signal will be referred to herein as a video information signal.
Video recorder-playback machines utilizing amplified light beams for recording and playback purposes offer significant advantages in that all physical contact of the recording and playback elements with the storage medium, namely, the information disc, is avoided. This prevents wear and deterioration of the machine elements and the disc, resulting in a high quality stored video signal which can be played back repeatably over a long period of time with unimpaired video resolution.
In video recorder-playback machines using amplified light beams for signal recording and playback, the recording and playback optical beams are focused upon the video information disc by a focusing lens which traverses the span of the disc in a radial direction simultaneously with relatively high speed rotation of the disc. In this manner, a spiral pattern of closely spaced tracks is formed on the disc to represent the video information. For maximum storage capacity for each disc, together with maximum signal resolution, the information tracks are formed to have a narrow width such as on the order of about 0.5 microns, and the center-to-center spacing between radially adjacent tracks in the spiraling pattern is on the order of about 1.5 microns. Accordingly, to prevent cross talk between the tracks during recording and/or playback operation, it is imperative that the video information disc be rotatably driven about an accurate and consistent axis of rotation to avoid substantial radial eccentricities.
In the prior art, a variety of drive spindle assemblies have been proposed for rotatably driving the video information disc. However, many of these prior art proposals involve so-called direct drive arrangements wherein a rotatable spindle carrying the disc is rotatably driven through a mechanical connection by a high speed drive motor. These direct drive arrangements tend to impart undesired system vibrations from the motor to the spindle to cause relatively slight radial excursions of the spindle during rotation which in turn frequently results in cross talk during operation of the machine. Some attempts have been made to isolate the spindle from this system vibration by at least partially supporting the spindle upon an air bearing. However, these arrangements have not heretofore proven totally satisfactory for eliminating cross talk between tracks during operation.
The present invention overcomes the problems and disadvantages of the prior art by providing an improved spindle assembly for a video recorder-playback machine. The improved spindle assembly includes a rotatable spindle shaft carried for consistent and high speed rotation about a vertical axis for accurate driving of a video information disc.